N mineralization process of the surface soils under shifting cultivation in Northern Thailand
1998
Tanaka, S. (Kyoto Prefectural Univ. (Japan). Faculty of Agriculture) | Funakawa, S. | Kaewkhongka, T. | Yonebayashi, K.
N mineralization process (ammonification plus nitrification) in the surface 0-5cm soil layers under shifting cultivation in northern Thailand was studied. Labile pool of organic matter extracted with a K2SO4 solution at 110 degrees C in an autoclave (fraction A) or by shaking at room temperature (fraction B) was used as factor to evaluate the N mineralization process which was examined in an incubation experiment. In the soils, in which the N mineralization pattern was fitted to a first order kinetics model, the content of (organic + NH4(+))-N in fraction B determined the initial rate of N mineralization. The soils, which showed a short lag time of less than 7 d both in the N mineralization and nitrification processes, had a high ratio of organic C to (organic + NH4(+))-N in fraction B, exceeding the value of 7. The soils, which showed a long lag time of more than 7 d only in the nitrification process, had a low pH(KCl) (less than 4.2). Thus, the rate of N mineralization was affected by the labile pool in fraction B or soil pH. On the other hand, there was a correlation between the No+Nmax (inorganic N at 0 d + maximum amount of mineralizable N) value and the labile pool in the fraction A, suggesting that the No + Nmax value depended on the contents of the labile pool
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